1. Field of the Invention
The present invention relates to a process for the production of resin extended pigments which exhibit improved dispersibility over the corresponding nonresin extended pigment in a variety of plastics applications.
Pigments are widely used in various types of polymeric media. The efficiency of a pigment as a color imparting substance is very dependent on the degree of pigment dispersion achieved in these media. Generally pigments are products having a very small particle size with a consequent tendency to form aggregates during their preparation. This tendency to form aggregates is particularly troublesome during the drying step used in the preparation of pigments. In order to overcome this tendency to form aggregates various methods have been used to prevent or minimize the formation of aggregates and thus enhance dispersibility of the pigment involved.
2. Prior Art
In U.S. Pat. No. 3,360,497 a series of pigment concentrates in polyolefins are disclosed for preparing fibers and films where a high degree of pigment dispersion is required. A pigment of reduced particle size is dispersed in water in a pebble mill in the presence of a surfactant. In a separate step the pigment dispersion is mixed with a low molecular weight polyolefin dissolved in a solvent to effect transfer of the pigment to the polyolefin-solvent phase. The low molecular weight polyolefin is then extended with a high molecular weight polyolefin, separated from the water and then dried.
U.S. Pat. No. 3,437,503 discloses salt milling a pigment together with a resinous substance such as rosin, chemically modified rosin or polymers or copolymers of alkyl vinyl benzenes.
U.S. Pat. No. 3,586,247 discloses preparation of resin extended pigments by grinding a mixture of pigment of pigmentary particle size and a normally solid carrier resin at a temperature above the melting point of the resin. On cooling a concentrate or resin extended pigment is obtained.
U.S. Pat. No. 3,748,164 discloses producing a pigment by grinding a mixture of crude organic pigment and an aminoplast tackifying agent selected from a group of certain urea derivatives with an inorganic salt grinding agent. Various additives such as liquids, surface active agents and solid resins can be included in the mixture.
U.S. Pat. No. 3,806,464 discloses a process of preparing a pigment encapsulated with an acrylic interpolymer by comilling the pigment, the acrylic interpolymer and a solvent for the acrylic interpolymer. After the comilling step the solvent is removed.